A140 Clutch/Gearbox problem?

[L*100]

I own an A140 Avantgarde ACS (2000/V) and a loud 'clunk' or 'thud' happens when I change gear, sounds like it is coming from the front of the car. This is only intermittent and although it mostly happens after long journeys at high speed it is becoming more frequent during 'normal' driving. It has done 69k and is well up-to-date with services etc. Garage I bought it from are stumped and thought I would try here before taking to MB or specialist...any ideas anyone?? p.s. I am not a mechanical person at all!!

 

[Dieselman]

Does it only do this when changing gear or when the power is applied and removed sharply.

If it's when changing gear only suspect the clutch, gearbox or driveshafts, if when applying and removing power suspect the engine mountings.

 

[L*100]

Hey Diesel, thanks for response! The 'clunking' noise only happens on gear change, as I put it in to gear opposed to pulling it out. It is one of those auto-clutch models, if I forgot to mention earlier

 

[Dieselman]

Hey Diesel, thanks for response! The 'clunking' noise only happens on gear change, as I put it in to gear opposed to pulling it out. It is one of those auto-clutch models, if I forgot to mention earlier

No you didn't.."I own an A140 Avantgarde ACS

It could be the clutch not fully releasing causing the gears to bang on meshing.
Difficult to say without seeing it.

Are the gears ever difficult to engage at rest or difficult to pull into neutural?

 

[L*100]

Occasionally it needs an extra push to get it in to 1st after coming to halt at junction - coming back in to neutral has not been a problem.

 

[Dieselman]

Sounds like the clutch is dragging. Suspect the CSC or master cylinder.

 

[L*100]

Many thanks Dieselman...I shall put this to my garage! :bannana:

 

[L*100]

Solution!

OK so after many more moans at my garage (and a 2 page long letter of complaint!) they finally took my poor A140 to Mercedes and they have found the problem to be a faulty Lambda O2 sensor...apparantly they are replacing both of them to to be safe...something about they tell the computer how hot the engine is which affects gear change?! Does this sound resonable to you more mechanical people??

 

[recycled]

no it doesnt.
might affect autos i doubt if that will affect a manual

 

[jaymanek]

its a semi auto and so may affect it... i should think the MAF may also be playing a part though...

 

[recycled]

oops sorry. then something has messed up the sensor. better to find that out before changing it.
dodgy maf/ fuel / fuel mixture

 

[jaymanek]

well lambda sensors are becoming quite a common replacement, all i will say is dont use cheap ones as they dont last and can often break up inside the exhaust!

 

[L*100]

I think (and hope!) that a Mercedes garage is doing the replacement so I would like to assume that they will put some good ones in. I am not really convinced that these sensor thingys are gonna fix my problem but I guess all I can do is wait and see if the problem occurs again. Thanks for your help so far guys, may call on you again!

 

[L*100]

Update!

OK so my baby benz has been back with me for about 3 weeks now with new Lambda O2 sensors. Have been on many journeys doing some testing and clunking noise has happened again!! Random gear changes again and it has even done it putting in to reverse whilst stationary. I am convinced now that the gearbox is on its way out (and I am sure that the temperature of engine plays a part?!) and I am very fed up...writing another letter of complaint to my garage insisting I have a refund or replacement car. It is a shame as I really enjoy driving it - when it is working correctly!!

 

[BlackC55]

I suspect the clutch is not operating properly. Have the system beld properly. (need a Star for that)